The present invention generally relates to recording and reproducing apparatus and, more particularly, to apparatus that is adapted to record and reproduce television signals, using digital techniques.
The continued advances in technology have resulted in many changes in the equipment that is currently being used in television broadcast stations. One of the more recent changes that has evolved is the shift away from photographic techniques toward the use of magnetic media in many phases of the operation of the commercial broadcast television station. For example, feature films being broadcast often originate from magnetic tape rather than film and television station news departments are increasingly converting to videotape recording systems rather than using film cameras to provide the visual coverage of the news stories. Moreover, many systems utilize travelling transmitters that can either broadcast on location coverage or transmit such coverage to the station which can either be broadcast "live" or videotaped, edited and broadcast at a later time. Some of the many benefits of these techniques are the ease of handling, flexibility and speed of processing compared to the use of photographic film, coupled with the ability to reuse the magnetic tape when the information that is recorded on them is no longer needed.
One of the last remaining film domains in the present day commercial television broadcasting station is the Telecine island which uses 35 millimeter film transparencies. The Telecine island is used to provide video still images that are used during programming, commercials, news and the like, i.e., wherever a still image may be used during operation. Their use is extensive as is evidenced by the fact that the average commercial broadcast television station maintains a total file on the order of about 2000 to 5000 35 millimeter transparency slides. The maintenance of the total file represents a laborious operation which requires introduction of new slides, the discarding of obsolete slides and the maintenance of an accurate index so that they can be readily obtained when needed. When slide program sequences are to be assembled, they must be manually carried to the Telecine island, cleaned and manually loaded. Even with the cleaning operation, dust particles and scratches and the like may easily result in an unsatisfactory end product even when the projectionist is careful. Moreover, following their use during broadcasting, the slides must be removed and returned to the file. The entire assembling, use and refiling of the slides represents a substantial labor investment because of the many manual operations that are required. The Telecine operation is considered to be one of the most antiquated operations in many modern broadcast stations and is basically incompatible with a fully automated station operation.
In contrast to the Telecine island or the use of opaque graphic material as the source for generating video still images, the present invention described herein facilitates the use of a recording and playback apparatus that will record and reproduce still images, with the still image video information being stored on magnetic media. The magnetic recording and playback apparatus utilizes generally standard computer disk drives (though modified in some respects) as the magnetic storage media and thereby eliminates the many problems that are associated with slide transparencies. Since the still images are recorded on magnetic media, the problems of physical degradation during use, e.g., dust particles and scratches, are not experienced. Moreover, since the recorded information can be easily accessed, the same still image may be used by operators at different locations almost simultaneously.
The present invention uses digital techniques to process color video information signals for recording and reproducing with respect to a record medium to generate special effects television displays. To generate such displays from a single or a number of television fields less than the number forming a color frame, it is desirable to separate the luminance and chrominance components forming the color video information signal and selectively invert the chrominance component to maintain the proper field-to-field color phase sequence in the color video information signal used to produce the special effects display. In digital color video information signal systems, comb filters are widely used to separate the luminance and chrominance components. Typically, the separation is accomplished by arithmetically combining quantized samples from at least three consecutive television lines of the same field at vertically aligned picture element locations in lines. If the color video information signal is sampled at a rate that is an odd multiple of the chrominance subcarrier frequency, the signal will be sampled during consecutive lines at different times relative to the start of the consecutive lines, or at times corresponding to picture element locations in the displayed signal that are not in vertical alignment.
To facilitate the separation of the luminance and chrominance components in digital video systems in which the color video information signal is sampled at a rate equal to an odd multiple of the subcarrier frequency, the present invention utilizes a particular sequence of phase reversed and phase continuous clock signals to control successive processing of the color video information signal. More specifically, the analog color video information signal is sampled at times determined by a first clock signal of a predetermined frequency whose phase is reversed on every consecutive horizontal line. The obtained samples are digitized and encoded for recording on a magnetic record medium. A phase continuous second clock signal at the predetermined frequency is utilized to clock the encoded data. Upon the reproduction of the encoded data, the data is decoded and reclocked relative to a third clock signal at the predetermined frequency whose phase is reversed on every consecutive horizontal line. Following reclocking, the chrominance component is separated from the composite color video data and selectively inverted. The selectively inverted chrominance component is combined with data from which it was separated to form a new composite digital color video signal. The new composite signal is converted to analog form using a fourth clock signal at the predetermined frequency whose phase is reversed on every consecutive horizontal line.
Processing color vido information signals under the control of the aforedescribed sequence of phase reversed and phase continuous clock signals results in obtaining samples at vertically aligned picture element locations in the horizontal lines while avoiding phase discontinuities in the signal that is recorded on the record medium. Furthermore, the sequence of clock signals is such that the samples of the color video information signal are in proper alignment for separating the luminance and chrominance components.